CASE REPORT

CASE REPORT
Print ISSN 1738-6586 / On-line ISSN 2005-5013
http://dx.doi.org/10.3988/jcn.2013.9.4.280
J Clin Neurol 2013;9:280-282
Open Access
A Case of GNE Myopathy Presenting a Rapid
Deterioration during Pregnancy
Jae Eun Sim,a Ji-Man Hong,a Gyoung Im Suh,a Hanna Cho,a
Kyung Seok Park,b Eun-Hee Sohn,c Young-Chul Choia
a
Department of Neurology, Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Korea
Department of Neurology, Seoul National University College of Medicine, Seoul, Korea
c
Department of Neurology, Chungnam National University College of Medicine, Daejeon, Korea
b
Received April 4, 2011
Revised July 10, 2012
Accepted July 10, 2012
Correspondence
Young-Chul Choi, MD, PhD
Department of Neurology,
Gangnam Severance Hospital,
Yonsei University
College of Medicine,
211 Eonju-ro, Gangnam-gu,
Seoul 135-720, Korea
Tel +82-2-2019-3323
Fax +82-2-3462-5904
E-mail [email protected]
BackgroundzzGNE myopathy is characterized by early-adult-onset distal myopathy sparing
quadriceps caused by mutations in the GNE gene encoding UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase, an enzyme in the sialic-acid synthesis pathway.
Case ReportzzA 27-year-old Korean woman presented a rapid deterioration in strength of the
distal lower limbs during her first pregnancy. She was diagnosed with GNE myopathy and carrying the compound heterozygous mutations of the GNE gene (D208N/M29T).
ConclusionszzThis is a representative case implying that an increased requirement of sialic acid
during pregnancy might trigger a clinical worsening of GNE myopathy.
J Clin Neurol 2013;9:280-282
Key WordszzGNE myopathy, GNE gene, sialic acid, pregnancy, hyposialylation.
Introduction
GNE myopathy, otherwise known as Nonaka myopathy or
hereditary inclusion-body myopathy, is an autosomal recessive myopathy characterized by weakness of the distal muscles in the lower limbs with preferential involvement of the
tibialis but a sparing of quadriceps muscles, with early-adult
onset at ages ranging from 15-40 years. The serum creatine
kinase (CK) level is normal or mildly elevated, and muscle
biopsy typically shows rimmed vacuoles (RV).1
GNE myopathy is caused by mutations in the gene encoding UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE). This gene encodes a bifunctional
protein with two enzymatic activities: UDP-GlcNAc2-epimerase and ManNAc kinase (MNK). Although the molecular
mechanism by which the mutations in the GNE gene cause
the muscle degeneration seen in GNE myopathy remains uncc This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Copyright © 2013 Korean Neurological Association
clear, it has been proposed that the mutations lead to defective sialylation of muscle. It has also been reported that there
is an increased requirement for sialic acid during pregnancy
in patients with GNE myopathy.
We describe a GNE myopathy patient carrying a GNE mutation (D208N/M29T) who presented a rapid deterioration in
strength of the distal lower limbs during pregnancy.
Case Report
A 27-year-old Korean woman complained of difficulty walking during her first pregnancy. She found it more comfortable
to walk on her toes than on her heels. She subsequently experienced impaired foot dorsiflexion with frequent falling and
rapid wasting of both anterior tibialis muscles during the third
trimester and following delivery. A review of her history revealed normal mental and physical development, and she reported no difficulties with daily activities prior to pregnancy.
Her family history was significant in having an older sister
with a similar progressive limb weakness, appearing in the
lower limbs at 19 years and in the upper limbs at. The neuro-
Sim JE et al.
logic examination of our case revealed marked weakness and
atrophy of both anterior tibialis muscles with no weakness of
the quadriceps and upper limbs. Motor strengths were decreased in ankle dorsiflexion [1/5 on the Medical Research
Council (MRC) Scale] and plantar flexion (4/5 on the MRC
Scale). She had normal deep tendon reflexes in all limbs without sensory deficit. She had no pathologic reflexes. The serum
CK level was slightly elevated to 302 U/L (normal range 21215 U/L). Electromyography revealed myopathic changes.
A computed tomography scan of her skeletal muscles
showed severe fatty infiltration of the gastrocnemius, soleus,
and tibialis anterior muscles with sparing of the quadriceps
muscles (Fig. 1). A muscle biopsy performed on the vastus
lateralis muscle revealed mild myopathic changes without
RV. After obtaining informed consent, 11 coding exons (exons
2- 12) of the GNE gene were analyzed, which revealed compound heterozygous mutations changing the ATG (methionine) to ACG (threonine) at codon 29 (M29T) in exon 2 and
the GAT (aspartic acid) to AAT (asparagine) at codon 208
(D208N) in exon 4 (Fig. 2).
A B Fig. 1. Images from a computed tomography scan of the patient’s
leg muscles. We observed severe fatty infiltration (white arrow) of
the gastrocnemius, soleus, and tibialis anterior muscles (B) compared to the quadriceps muscles (A), which were unaffected.
A B Fig. 2. Mutation analysis of GNE (black arrowheads): (A) c.86T>C
in exon 2 (M29T) and (B) c.622G>A in exon 4 (D208N).
Discussion
UDP-GlcNAc2-epimerase catalyzes the rate-limiting step in
sialic acid biosynthesis and MNK catalyzes the subsequent
step. Sialic acids, which are N-acetylated derivatives of neuraminic acid, are the most abundant terminal monosaccharides
on the glycoconjugates of eukaryotic cell surfaces, and they
play important roles in development, regeneration, and biomedical functioning.2,3
The main pathophysiology involved in GNE myopathy is
hyposialylation and abnormal glycosylation, which may lead
to the misfolding of some glycoproteins. Noguchi et al.4 demonstrated that the levels of sialic acid in muscles and primary
cultured cells from GNE myopathy patients were reduced by
60-75% compared to healthy controls. Correction of this hyposialylation has been attempted in GNE myopathy mice and
could led to a therapeutic strategy for human patients.5 The sialylation status in skeletal muscle tissue is also greatly altered,
especially in the fibers with RV, suggesting a close relationship between hyposialylation and the formation of RV.4,6
We have reported a Korean patient with GNE myopathy
who carried the compound heterozygous mutation of the
epimerase domain of the GNE gene. Although the M29T mutation has been reported previously,7 the D208N mutation
found in the present case is novel. Various GNE mutations
have been identified in GNE myopathy patients from various
ethnic groups. The M712T mutation is the most common mutation in Jewish hereditary inclusion-body myopathy, while
the most frequent mutation in Japanese and Korean GNE myopathy patients is the V572L mutation, which suggests that a
common founder effect exists in these populations.
It was especially interesting that our patient experienced
rapid deterioration in muscle strength during her first pregnancy. Similar cases have been reported previously.8,9 Sialic acid
is known to be essential for embryonic development.10 and it
has been suggested that the elevated sialic acid level in pregnant women and the high level of GNE expression in the placenta may indicate an increased requirement for sialic acid
during pregnancy. The lower levels of sialic acid in women
with GNE myopathy compared to healthy controls could explain the clinical deterioration during pregnancy observed in
our patient. We therefore suggest that the rapid progression of
muscle weakness in our patient during pregnancy may be explained by hyposialylation11 and abnormal glycosylation associated with GNE myopathy and an increased requirement
for sialic acid during pregnancy.
We have reported a representative case with rapid deterioration in muscle strength during pregnancy in GNE myopathy. However, future studies should involve more patients and
address causality in order to allow definitive conclusions to
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A Case of GNE Myopathy with Pregnancy
be drawn.
Conflicts of Interest
The authors have no financial conflicts of interest.
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